Dwarfism, a mendelian recessive character of the mouse, w a s reported by Siiell ('29). Later studies by Smith and MacDowell ( '30, '31) showed that in such dwarfs the anterior pituitary lacked typical eosiiiophile cells and their experimental studies demonstrated that the gonad-stimulating hormone was present in relatively high concentration, while the growth hormone was suppressed.
The dwarfs were sterile. However, in the male dwarfs the reproductive sys tern was relatively well cliff er cnt ia t ed, motile sperm were present in the testes and the accessory glands were normal. In dwarf females the reproductive system was not so advanced. Cavity formation in the ovarian follicles w a s rare, the uteriis was infantile, and the vaginal orifice was probably not established. The dwarfism appears abruptly at about the fifteenth clay of postnatal life.
In view of the marked retardation of growth, it seemed of interest to study the effect of this naturally occurring anteriorpituitary disability on the differentiation of the skeleton, espccially with reference to the question of epiphyseal union. Dwarfs and their normal litter mates, secured through the kindness of Dr. Gregory Piiicus and Dr. Alfred Marshak, were used in this study. The animals ranged in age from 6 weeks to 8 months. Attention was focused chiefly on the fore axid hind limbs, although supplementary observations were made on the 485